INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Details) - Fixed maturity securities - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		$ 10,781
Total Unrealized Losses		481
Less than 12 months Fair Value		6,902
Less than 12 months Unrealized Losses		184
12 months or longer Fair Value		3,879
12 months or longer Unrealized Losses		297
Total Fair Value	$ 7,190
Total Unrealized Losses	385
Less than 12 months Fair Value	3,423
Less Than 12 months Unrealized Losses	178
12 months or longer Fair Value	3,767
12 months or longer Unrealized Losses	207
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		2,604
Total Unrealized Losses		52
Less than 12 months Fair Value		2,604
Less than 12 months Unrealized Losses		52
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		183
Total Unrealized Losses		5
Less than 12 months Fair Value		169
Less than 12 months Unrealized Losses		4
12 months or longer Fair Value		14
12 months or longer Unrealized Losses		1
Total Fair Value	80
Total Unrealized Losses	3
Less than 12 months Fair Value	80
Less Than 12 months Unrealized Losses	3
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		37
Total Unrealized Losses		1
Less than 12 months Fair Value		37
Less than 12 months Unrealized Losses		1
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		135
Total Unrealized Losses		1
Less than 12 months Fair Value		135
Less than 12 months Unrealized Losses		1
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		1,809
Total Unrealized Losses		102
Less than 12 months Fair Value		765
Less than 12 months Unrealized Losses		36
12 months or longer Fair Value		1,044
12 months or longer Unrealized Losses		66
Total Fair Value	1,828
Total Unrealized Losses	89
Less than 12 months Fair Value	1,828
Less Than 12 months Unrealized Losses	89
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		613
Total Unrealized Losses		37
Less than 12 months Fair Value		290
Less than 12 months Unrealized Losses		13
12 months or longer Fair Value		323
12 months or longer Unrealized Losses		24
Total Fair Value	636
Total Unrealized Losses	31
Less than 12 months Fair Value	636
Less Than 12 months Unrealized Losses	31
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Dollar-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		94
Total Unrealized Losses		2
Less than 12 months Fair Value		94
Less than 12 months Unrealized Losses		2
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Dollar-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		360
Total Unrealized Losses		5
Less than 12 months Fair Value		360
Less than 12 months Unrealized Losses		5
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Dollar-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		326
Total Unrealized Losses		15
Less than 12 months Fair Value		208
Less than 12 months Unrealized Losses		7
12 months or longer Fair Value		118
12 months or longer Unrealized Losses		8
Total Fair Value	306
Total Unrealized Losses	10
Less than 12 months Fair Value	69
Less Than 12 months Unrealized Losses	2
12 months or longer Fair Value	237
12 months or longer Unrealized Losses	8
Dollar-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		39
Total Unrealized Losses		3
Less than 12 months Fair Value		39
Less than 12 months Unrealized Losses		3
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		82
Total Unrealized Losses		7
Less than 12 months Fair Value		44
Less than 12 months Unrealized Losses		1
12 months or longer Fair Value		38
12 months or longer Unrealized Losses		6
Total Fair Value	79
Total Unrealized Losses	4
Less than 12 months Fair Value	18
Less Than 12 months Unrealized Losses	0
12 months or longer Fair Value	61
12 months or longer Unrealized Losses	4
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		4,499
Total Unrealized Losses		251
Less than 12 months Fair Value		2,157
Less than 12 months Unrealized Losses		59
12 months or longer Fair Value		2,342
12 months or longer Unrealized Losses		$ 192
Total Fair Value	4,261
Total Unrealized Losses	248
Less than 12 months Fair Value	792
Less Than 12 months Unrealized Losses	53
12 months or longer Fair Value	3,469
12 months or longer Unrealized Losses	$ 195